Patent Literature 1 describes a bidirectional step-up/step-down chopper circuit which is of isolated type and which is connected between a battery and an electric double layer capacitor. The bidirectional step-up/step-down chopper circuit described in Patent Literature 1 includes a transformer provided with center taps. The center tap of a primary-side winding wire of the transformer is connected to a positive side of the battery via a reactor, and both ends of the primary-side winding wire are connected to a negative side of the battery via respective step-up chopper elements. The center tap of a secondary-side winding wire of the transformer is connected to one end of the electric double layer capacitor, and both ends of the secondary-side winding wire are connected to the other end of the electric double layer capacitor via respective step-down chopper elements. Moreover, between input terminals of the bidirectional step-up/step-down chopper circuit, a smoothing capacitor is connected.
It is, however, desirable in a bidirectional step-up/step-down chopper circuit (converter circuit) as described in Patent Literature 1, to reduce an inrush current to a (smoothing) capacitor when a direct-current power supply (battery) is electrically connected to the capacitor.